Disc drives are data storage devices that store digital data in optical/magnetic form on a rotating storage medium. Modern magnetic disc drives comprise one or more information storage discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator for movement of the heads in an arc across the surface of the discs. Each of the concentric tracks on each surface is generally divided into a plurality of separately addressable data sectors. The recording transducer, e.g. a head carrying a magnetoresistive read element and an inductive write element, is often referred to as a read/write head. The head is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to a host computing system. The overall capacity of the disc drive to store information is dependent upon the disc drive recording density.
The transducers (heads) are mounted on gimbals and supported via flexures at the distal ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a shaft mounted to the disc drive base plate at a position closely adjacent the outer edges of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the transducers move in planes parallel with the surfaces of the discs.
Such rotary actuators typically employ a voice coil motor to position the transducers with respect to the disc surfaces. The actuator voice coil motor includes a voice coil extending or projecting from the actuator body in a direction opposite the actuator arms and immersed in the magnetic field formed by one or two bipolar permanent magnets. When controlled direct current is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the transducers move across the disc surfaces. The actuator thus allows the transducers to move back and forth in an arcuate fashion between an inner diameter and an outer diameter of the disc stack.
The transducers sequentially write data to tracks on the disc surface. When the transducer that is executing the write operation reaches the end of a track, the transducer ceases execution of the write operation. The actuator positions the transducer over an adjacent track on the same disc surface, or a “head switch” is performed, i.e., a different transducer is selected to receive the incoming write signals and the write operation is executed on a different disc surface.
In one head switch pattern, the transducers sequentially execute write operations on aligned tracks of corresponding disc surfaces. A head switch is performed each time a track is full. The actuator positions the transducers in alignment with the adjacent tracks after a group of aligned tracks are full. The head switches continue in sequence as the aligned tracks become full. The actuator continues positioning the transducers in alignment with adjacent tracks. The write operations are sequentially executed in accordance with the head switches until the write operation is complete.
Track pitch on a disc has become progressively smaller as disc drive capacities increase. The minute track pitch hinders the actuator from precisely aligning the transducer with the subsequent track from one disc surface to the next. To overcome this problem, each head switch is followed by an actuator seek operation to align the transducer with the appropriate track. An actuator seek operation executed after a head switch substantially decreases the efficiency of disc drive performance.
An existing method for executing a write operation implements a “serpentine” format of actuator movement and head switches. Each disc surface is partitioned into a number of concentric regions such that each region includes several tracks. The actuator positions the transducer above a track on an upper disc surface. The transducer executes a write operation until the track is full. The write operation ceases as the actuator moves toward an inner boundary of the region to position the transducer in alignment with an adjacent track. The transducer continues executing the write operation on the adjacent track until the track is full. The actuator moves toward the inner boundary of the region to position the transducer in alignment with subsequent adjacent tracks after each track is filled.
A head switch is performed when the track on the upper disc surface adjacent to the inner boundary of the region is full. The transducer executes a write operation on a track on a lower disc surface adjacent to the inner boundary of the region until the track is full. The write operation ceases and the actuator moves toward an outer boundary of the region to position the transducer in alignment with an adjacent track. The transducer executes the write operation on the aligned track until the track is full. The actuator moves toward the outer boundary of the region to position the transducer in alignment with subsequent adjacent tracks after each aligned track is full. A head switch is performed when the track adjacent to the outer boundary of the region is full. The “serpentine” format is repeated on the remaining disc surfaces until the write operation is complete.
The execution of sequential write operations within a region before performing a head switch minimizes the number of head switches and actuator seek operations during a write operation. After a head switch is performed, the transducer is misaligned with the sequential track by an average of 10 tracks due to the fine track pitch on the disc surface. In a disc drive having an even number of disc surfaces, a seek operation is required after one complete serpentine iteration to determine the start location of the next iteration. Thus, different formats are required for odd and even number of disc surfaces. Furthermore, the serpentine format described requires the ability to increment logically in both inner and outer directions on a disc surface. Against this backdrop the present invention has been developed.